Piezoelectric record cutting stylus

ABSTRACT

For cutting mechanical recordings in a flat record carrier with a recording frequency of 20 to 200-400 kHz, a piezoelectric transducer arranged to undergo longitudinal oscillations to drive a cutting stylus, the transducer being constituted by a body of an amorphous piezo oxide composed of a mixture of oxides of lead, zirconium and titanium and having a coupling coefficient of at least about 0.6 and a mechanical resonant frequency above the highest frequency to be recorded, the transducer being connected to an electric signal supply circuit having a high electrical resistance such that the combination of the high electrical resistance and the high coupling coefficient of the transducer results in a maximum resonance gain in the transducer response of no more than 10 db.

. United States Patent [191 Klemp et al.

[111 3,805,100 [451 Apr. 16,1974

1 1 PIEZOELECTRIC RECORD CUTTING STYLUS [75] Inventors: Hans-Joachim Klemp; Horst Redlich, both of Berlin, Germany [73] Assignee: Ted Bildplatten Aktiengesellschaft Aeg-Telefunken, Teldec, Zurich, Switzerland 22 Filed: I Jan. 17, 1973 21 Appl. 190.; 324,407

30 Foreign Application Priority Data Jan. 22, 1972 Germany 2203095 QQFWPY; "11:77." t": 7202409 [52] US. Cl. 310/8.3, 179/100.4 C, 179/100.41 P,

- 274/46, 310/82, 310/94 [51] .Int. CL... H04r 17/00, H04r 17/02, G1 1b 3/00 [58] Field of Search ..310/8.3, 8.1, 9.4, 8.2; 179/100.4 C, 100.41 P; 2.74/38, 46, 42

Jan. 22, 1972 [5 6 References Cited UNITED STATES PATENTS 1,737,253 11/1929 Linsell l79/l0O.41 P

1,980,888 11/1934 Thomas. 2,449,291 9/1948 Gay 3,490,771 1/1970 Bauer 179/l00.4 C 3,652,809 3/1972 Dickopp et a1 l79/l00.41 P 3,691,318 9/1972 Schuller et al. 179/100.4l P

Primary Examiner-J. D. Miller Assistant Examiner-Mark O. Budd Attorney, Agent, or Firm--George H. Spencer 57 ABSTRACT For cutting mechanical recordings in a flat record car rier with a recording frequency of 20 to 200-400 kHz, a piezoelectric transducer arranged to undergo longitudinal oscillations to drive a cutting stylus, the transducer being constituted by a body of an amorphous piezo oxide composed of a mixture of oxides of lead, zirconium and titanium and having a coupling coefficient of at least about 0.6 and a mechanical resonant 13 Claims, 4 Drawing Figures PIEZOELECTRIC RECORD CUTTING STYLUS BACKGROUND OF THE INVENTION The present invention relates to record cutters, particularly for operation at recording frequencies I of -400 kHz.

It is known to mechanically record sound oscillations having an upper frequency limit of about 20,000 Hz on the prior art and are disclosed, for example, in the following publications:

Radio Mentor, Issue No. 7, 1970, pages 451452; VDl-Nachrichten, Issue No. 26, July 1, 1970, page 1; I Radio Mentor, Issue No. '8, 1970, pages 51 3-5 16; I German Patent No. 1,574,489.

Because of the wide frequency range which must be covered in the recording of video signals, for example when recording a moving image, the playback of such a video recording must take place at relatively'high playback speeds (up to 1,500 rpm for a 200 mm record) compared tothe usual sound recordings.

It is obvious, however, that the recording of such video programs, which-is effected with mechanically, electrodynamically or electrostatically controlled recording-devices, cannot take place at the same speed because the member which produces the undulations in the recording groove to correspond to the signals could never follow the high frequencies (up to 4 MHz) to be recorded due to its inherent mass inertia. Thus a video record, or a matrix for such a video record, is produced with the aid of an intermediate recording of the signals, a technique known from the manufacture of sound records, for example on a magnetic carrier. This carrieris scanned at a speed reduced by about ten to times,

' compared to the real-time speed, so that for an upper frequency limit of the playback signals of about 4 MHz, the recording device must be able to produce perfect recordings to about 160 to 400 kHz.

- In spite of the substantially reduced recording speed, this upper frequency limit is still extremely high for an instrument which must produce mechanical undula- -,tions in the recording groove of a signal carrier. Even high-quality instruments built for special purposes presently have an upper recording frequency limitof about to 40 kHz.

SUMMARY OF THE INVENTION tion of the resonance gain. The high dielectric constant.

oxide having a high longitudinal coupling cocfficient of about 0.6 or'more andis made ofa mixture of metal oxides, in particular oxides of lead, zirconium and titanium. Moreover, the transducer is so dimensioned that its natural mechanical resonant frequency lies somewhat above the highest frequencyto be recorded and the ohmic resistance of the electrical current supply circuit for the transducer is selected so that the resonance gain due to the natural resonance of the transducer in conjunction with the high coupling coefficient will be no more than 10 db above the minimum gain occurring in the range of the frequencies to be recorded.

A piezo oxide suitable for this purpose is manufactured, for example, by the firm Philips under the name Piezo Oxide PXES or by the firm Rosenthal under thenantefiSoncx .4J. 1 s: ma t of this id the powdery starting materials, i.e., the oxides of lead, zirconium and titanium, are mixed together and stirred in a finely ground wet state. After filtering and drying they are heated to 850 C so that the-components react and form a bond. Thereafter, the mass is again wet ground until a certain grain size has beenattained. After renewed filtering and drying, there is obtained a finished powder which can be brought into the desired shape, for example by pressing in matrices after the addition of small amounts of binder andsome water. Then follows the sintering process at 1,100" C which lasts for several hours. Thereafter, the ceramic bodies are mechanically machined, i.e., ground or sawed, in order to obtain the desired shapes and dimensions. Finally, the bodies, which thus far have no piezoelectric properties, are polarized by a direct voltage, while at an increased temperature of 300 C, with an electrical fieldstrength of about 1 to 5 kV/mm, preferably 3 kV/mm.

The ,thus obtained piezoelectric bodies have a frequency constant of about 1,500 Hz m, a longitudinal coupling coefficient between 0.6 and 0.7 and a relative dielectric constant of more than 1,000. This frequency constant for a cube with sides of 5 mm or for a cylinder 'with a diameter of 5 mm and a height of 5 mm results is desired in order tobe able to apply a lower voltage. A further advantage is the relatively high internal attenuation of the amorphous material. While an oscillator of a homogeneous material, such as quartz, may have a quality, 0, i.e., a resonance. gain of 1,000 and more, the Q of the amorphous oscillator having the abovelisted ingredients is only 50, for example.

By selecting the appropriate materials to be combined, it is possible, in contradistinction to naturally occurring homogeneous materials, to set the Q to any desired value, as has been done in the commercially available piezo oxides.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an oscillator according to the invention with a cutting stylus attached thereto, to a scale being considerably larger than life size.

FIG. 2 is an elevational view of the mounting of the oscillator of FIG. 1.

FIG. 3 is a basic circuit diagram of the oscillator nal input.

FIG. 4 is'a diagram used in explaining the contribution of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure shown in FIG. 1 includes a longitudinal oscillator 1 made of a piezo oxide with the abovementioned composition of oxides of lead, zirconium and titanium. Its longitudinal oscillations are shown in the direction of the double arrow and result in move ments of its top and bottom edges between the limits represented by the dashed lines. A stylus 2 is inserted in a tube 3 having high mechanical stability and good heat-conducting properties. Tube 3 is rigidly con nected, eg by welding, with a metal plate 4 which is soldered to oscillator l. Stylus 2 is commonly made of a diamond.

In order to facilitate the cutting process, the stylus 2 is heated to a relatively high temperature of about 100 C by means of a heating coil 8 which is fed by the heating current source H.

Oscillator 1 is held at its ends, according to the illustration shown to a somewhat smaller scale in FIG. 2, by

. means of springs 5. It is mounted to oscillate freely, to

float so to speak. The natural resonance of the resonant system including the mass of the oscillator 1 and the mass of springs as well as the elasticity of springs 5 must lie below the frequency range to be recorded. The information signal voltage to be recorded is fed in via springs 5 and silver electrodes at oscillator l.

The springs are advisably asymmetric three-armed springs whose center arm is oriented at 90 with respect to the other two arms, the latter extending in respectively opposite directions and the transducer being held at the point of intersection of the arms. Instead of the springs, membranes can also be used.

The natural oscillation of this mechanical oscillating system can be attenuated by a damping ring 9 of a damping material, such as rubber or plastic, disposed in the vicini ty of the zero oscillation point,or node, 10 of transducer 1.

Oscillator l is fed bya signal current source 7, as shown in FIG. 3, with a signal voltage of about 1.5 kV, via a relatively high resistance 6 of about 50 k0. This high resistance 6, together with the coupling coefficient, has the result that the natural resonance of the oscillator l which lies somewhat above the frequency range to be recorded is sufficiently attenuated so that the resonance gain will be no more than about 10 db.

It should be noted in this connection that the sum of this resistance 6 and the internal resistance of the current supply source must be considered for this attenuation effect. This sum must be greater than 50 k0. Under certain circumstances, and with an appropriate design of the circuit, a high internal resistance of the current supply source may be sufficient by itself, or only a relatively small resistance need be connected in series.

For reasons of circuitry it may be advantageous at times, however, to use a high resistance with the above given valve in the current supply circuit.

This resistance 6 also causes the oscillator 1 to be excited by a constant current (about to mA) practically over the entire frequency range. With the selected dimension of about 5 mm in the oscillation direction and with the material selected for the oscillator there sigresults a capacitance of about 150 pF between the electrodes of the transducer at a natural resonance frequency in the range of 300 to 350 kHz.

These dimensions produces a mechanical oscillation amplitude vs. frequency response A at stylus 2, for a set resistance value 6, having the form shown in FIG. 4.

Due to the capacitive reactance which increases toward low frequencies, the voltage across transducer 1 increases and thus, due to the constant current, the energy which is fed to the transducer results in the illustrated gain in amplitude for stylus 2 toward the lower frequencies. This is particularly desired in frequency modulation recordings since it will inherently raise the lower sideband, which has favorable effects during playback.

The oscillation amplitude is between about 0.3 and 0.5 [L at about 150 kHz and increases again, due to the natural resonance, inthe higher frequency range. This natural resonance, however, is sufficiently attenuated by the high electrical resistance provided according to the present invention in conjunction with the high coupling factor, as shown by the solid curve. The dashed curve R indicates the path that would exist without these attenuation measures. 7

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations and the same are intended to be comprehended within the meaning and range of equivalents of the appended 'claims.

We claim:

1. A piezoelectric transducer unit for driving a cutting stylus in a system for mechanically recording oscillations varying in frequency between 20 and 200-400 k-I-Iz, comprising a transducer constituting a longitudinal oscillator formed of a body of an amorphous piezo oxide having a high longitudinal coupling coefficient of at least about 0.6 and made of a mixture metal oxides, said body being dimensioned'such that its natural mechanical resonant frequency lies above the highest frequency to be recorded and an electric signal supply circuit whose ohmic resistance is such that the natural resonance of said transducer in conjunction with the high coupling coefficient results in a maximum resonance gain of no more than 10 db.

2. A device as defined in claim 1 wherein said oxide v is a mixture of oxides of lead, zirconium and titanium.

3. A device as defined in claim 1 wherein said circuit includes a current supply source and the ohmic resistance of said current supply circuit is formed by the internal resistance of said current supply source.

4. A device as defined in claim 1 wherein said circuit comprises a high resistance resistor connected in series therein.

5. A device as defined in claim 4 wherein the resistance of said resistor is substantially equal to the capacitive reactance of said transducer at a given frequency below the lowest frequency to be recorded.

6. A device as defined in claim 1 wherein said transducer is a cylinder and is no longer than approximately 5 mm in its longitudinal direction.

7. A device as defined in claim 1 wherein said transducer is a cube and is no longer than approximately 5 mm in its longitudinal direction.

8. A device as defined in claim 1 wherein the relative dielectric constant of the piezo material of said transducer is greater than 1,000.

9. A device as defined in claim 1 wherein the Q factor of the piezo material of said transducer is about 50.

10. A device as defined in claim 1, further comprising springs supporting said transducer at the longitudinal ends thereof.

11. A device as defined in claim wherein the natural resonance of the oscillating system constituted by the vibrating masses of said transducer and said springs,

and the elasticity of said springs, lies below the frequency range to be recorded.

12. A device as defined in claim 11, further comprispoint of intersection of said arms. 

1. A piezoelectric transducer unit for driving a cutting stylus in a system for mechanically recording oscillations varying in frequency between 20 and 200-400 kHz, comprising a transducer constituting a longitudinal oscillator formed of a body of an amorphous piezo oxide having a high longitudinal coupling coefficient of at least about 0.6 and made of a mixture metal oxides, said body being dimensioned such that its natural mechanical resonant frequency lies above the highest frequency to be recorded and an electric signal supply circuit whose ohmic resistance is such that the natural resonance of said transducer in conjunction with the high coupling coefficient results in a maximum resonance gain of no more than 10 db.
 2. A device as defined in claim 1 wherein said oxide is a mixture of oxides of lead, zirconium and titanium.
 3. A device as defined in claim 1 wherein said circuit includes a current supply source and the ohmic resistance of said current supply circuit is formed by the internal resistance of said current supply source.
 4. A device as defined in claim 1 wherein said circuit comprises a high resistance resistor connected in series therein.
 5. A device as defined in claim 4 wherein the resistance of said resistor is substantially equal to the capacitive reactance of said transducer at a given frequency below the lowest frequency to be recorded.
 6. A device as defined in claim 1 wherein said transducer is a cylinder and is no longer than approximately 5 mm in its longitudinal direction.
 7. A device as defined in claim 1 wherein said transducer is a cube and is no longer than approximately 5 mm in its longitudinal direction.
 8. A device as defined in claim 1 wherein the relative dielectric constant of the piezo material of said transducer is greater than 1,000.
 9. A device as defined in claim 1 wherein the Q factor of the piezo material of said transducer is about
 50. 10. A device as defined in claim 1, further comprising springs supporting said transducer at the longitudinal ends thereof.
 11. A device as defined in claim 10 wherein the natural resonance of the oscillating system constituted by the vibrating masses of said transducer and said springs, and the elasticity of said springs, lies below the frequency range to be recorded.
 12. A device as defined in claim 11, further Comprising a body of damping material supporting said transducer in the vicinity of its zero oscillation point for damping the natural resonance of said transducer.
 13. A device as defined in claim 10 wherein said springs each comprise asymmetrical three-armed springs whose center arm is oriented at 90* with respect to the other two arms, which extend in respectively opposite directions, and holding said transducer at the point of intersection of said arms. 